Mercury reservoir for discharge lamps



Jan. 24, 19 M. PENNYBACKER EI'AL 2,969,476

MERCURY RESERVOIR FOR DISCHARGE LAMPS Filed Sept. 19, 1957 INVENTOR.MILES PENNYBACKER CHARLES A. SIMPSON 2px K 4 4% THEIR ATTORNEY- UnitedStates MERCURY RESERVOIR FOR DISCHARGE LAMPS Filed Sept. 19, 1957, Ser.No. 684,923

2 Claims. (Cl. 313-328) This invention relates to mercury-gas dischargetubes for lighting and for advertising displays and relates moreparticularly to an improved means for providing a partitioned cavity atthe end of such tubes. This application constitutes acontinuation-in-part of my co-pending application Serial No. 618,636,filed October 26, 1956.

Discharge tubes of this general character are provided at each end withan electrode. The electrode is usually of the well-known cold cathodetype if the tube is intended to carry currents of up to about 200milliamperes and it is usually of the hot cathode type for highercurrents. The design and construction of the partitioned cavity of thisinvention is very similar for all types of such tubes. It performs oneor all of its several functions depending, among other things, upon thecurrent at which the tube operates, and the ambient temperature. Forexample, if the mercury discharge tube is of the cold cathode type andis operated outdoors in cold weather the cavity serves as a mercuryreservoir and prevents the loss of mercury vapor near the ends of thetube with consequent dimming at the ends which might otherwise occur. Inthis case it tends to increase the mercury vapor pressure. If the tubeis a hot cathode or a cold cathode fluorescent lamp operating atrelatively high current so that the wall temperature of the bulb in theportion between the electrodes is above that corresponding to optimummercury vapor pressure for best luminous efiiciency, then thepartitioned cavity serves to reduce the mercury vapor pressure by virtueof the fact that the insulated cavity is cooler than the rest of thebulb. In a particular lamp the cavity may perform first one of the abovefunctions and then the other. It may provide increased mercury vaporpressure at the end of the lamp if the lamp is operated at a low bulbwall temperature, and it may reduce the pressure of said vapor if thelamp is operated at a relatively high temperature.

in all cases the partition of our invention forms a cavity in which areserve of liquid mercury may be stored. This is important to a longlife of the lamp inasmuch as mercury is used up slowly during normaloperation. If this relatively large reserve supply is put into anordinary lamp not provided with a reservoir it frequently settles in theluminous portion of the lamp. It is then unsightly and reducesefiiciency. With the partition of our invention any such excess ofliquid mercury that gets into the luminous portion of the lamp duringmanufacture or later may be moved readily into the cavity of ourinvention where it is then effectively restrained from returning.

An object of this invention is to provide a partition which may becheaply formed of metal by a punch press operation, which does notrequire a seal or special close fit with the glass wall in order tosufiiciently restrict the flow of liquid mercury, which is shaped sothat the relation of its periphery to the glass wall facilitates theatent O F 2,969,476 Patented Jan. 24, 1961 ice passage of liquid mercuryin one direction and resists such passage in the other direction.

Another object of the invention is to provide a mercurygas dischargetube with a partitioned cavity wherein the lead-in-wires are insulatedfrom the cavity walls and particularly from the metal partition formingthe inner wall of the cavity.

The technique of fabricating and pumping the various types of gasdischarge tubes varies somewhat. In the standard hot cathode lamps thefilament is typically mounted on support wires which are sealed into thepressed section of a glass stem. This stem is then sealed onto the endof a fluorescent coated glass tube or bulb. The partition of ourinvention is mounted on the stem prior to the mounting of the filamentand with the supports extending through the partition through smallholes therein, or through eyelets so that passage of liquid mercury ineither direction would be prevented; It is necessary that one of thesupport wires be provided with a glass bead, a ceramic coating or otherinsulation so that a low voltage may be applied across the filamentwithout being short circuited by the partition or by the drop of mercurywhich may be accumulated in the cupped portion if the lamp is vertical.The pumping of the lamp and the insertion of mercury during the pumpingoperation may then be done in the usual manner.

Whenever the partitioned cavity is used on lamps intended primarily forindoor use, the cavity is needed only at one end of the lamp. This istrue because on these lamps the temperature of the main bulb portion isadequate to maintain adequate mercury vapor pressure, and a coolercavity at one end only is sufficient to reduce the mercury vaporpressure. The introduction of mercury during the pumping operation onsuch lamps may be done at either end. If the mercury is introduced intothe cavity during this operation it will vaporize or distill out insufficient quantity during the operation of the lamp. If mercury isintroduced at the other end, or into the main body of the lamp, it maybe forced past the partition and into the cavity by a shaking or tappingoperation as described below for sign tubes.

Mercury discharge tubes for outdoor signs, and lamps intended for use atlow ambient temperatures, will preferably have the cavity, or mercuryreservoir, provided at each end to prevent the end dimming which mightotherwise occur. While it is possible to provide tubulations at each endfor. the introduction of mercury into each cavity separately during thepumping operation, this invention also permits the introduction ofmercury without substantially altering the widely used method ofintroducing mercury directly into the main body of the tube rather thanthrough the electrode.

For example, in sign tube production it is common practice to seal asmaller diameter glass tube, known as the tubulation, at right angles tothe sign tube somewhere between the two electrodes. At the proper stagein the processing of the tube the mercury charge, usually consisting ofabout one or two grams of liquid mercury, is introduced by way of thistubulation. The tubulation is then sealed off with a gas flame. Asimilar procedure is used with tubes having electrodes of this inventionexcept that a charge of mercury about double the usual size ispreferred.

It has previously been proposed to provide a partition back of theelectrode consisting of a disc having its periphery sealed to or closelyfitting the glass wall with a mercury tight seal. The disc is providedwith one or more eyelets spaced at some distance from the periphery, thetubular portion of the eyelet extending into the reservoir. Thisaccomplishes the purpose of maintaining some liquid mercury in thereservoir regardless of ordinary handling. But it makes extremelydifiicult, if not impractical, the introduction of mercury from thecentral portion of the tube by the usual method described above. Theintroduction of mercury is facilitated by having the passages formercury along the glass wall of the tube as provided in this invention.After the mercury is introduced from the tubulation as described aboveit is then positioned on top of the partition adjacent to the tube wall,and hence over the open passages or ports in the partition. The tube isthen tapped or shaken to force all or part of the mercury through.Obviously it would be much more difficult to hold the mercury globuleover the opening of an eyelet in a flat disc during this operation.

The partition member of the present invention consists of one or aplurality of dished or cup-like structures preferably having a scallopedcontour around their periphery. Whereas one such cup gives good resultsit is preferred to employ at least two of the cups in nested relation,the openings between the cup and the glass wall being small enough toprevent the free flow of mercury should small particles get into theopenings. A considerable restraining force, however, comes from thecup-like shape of the partition, the concave side of the cup facing theadjacent closed end of the tube. If one end of the tube is placeddownwardly and then inverted the mercury will flow due to gravity butthe cup simply scoops up the globule of mercury. Even with the heavyvibration sometimes en countered in shipment or handling of the tube atleast some of the liquid mercury stays in the reservoir. It is thisresidue, however, small, which is important to the maintenance ofbrilliance in cold weather. Any excess mercury which goes into the mainportion of the tube is of little importance. Mercury vapor, however, canreadily pass through the openings. The partition of the presentinvention is thus essentially a one-Way or check valve since it deniestravel of the liquid mercury in one direction while permitting itspassage in the opposite direction and it accomplishes these resultswithout any moving parts.

In the drawing:

Fig. l is a broken side elevation, partially in section, of an electrodepositioned at one end of a tubular envelope for a mercury lamp embodyingthe present invention.

Fig. 2 is an elevation of the inner or convex end of one of thecup-shaped partitions.

Fig. 3 is a side elevation thereof.

Fig. 4 is a broken plan view of the outer or concave end of thepartition and showing a modified construction.

Fig. 5 is a section taken on line 55 of Fig. 4.

Fig. 6 is a broken side elevation of a hot cathode type of mercury lampwhere the electrode is not a separately formed element and thepartitions are located just outside the filament.

Fig. 7 is an electrode similar in construction to that of Fig. 1 exceptthat an insulating sleeve surrounds the two wires to insulate the cupsfrom the metallic circuit.

The tubular glass envelope is shown at 7 and it may have an internalcoating of fluorescent material which converts invisible ultra-violetrays from the mercury discharge into useful visible radiation. One endonly of the tube is shown as fitted with an electrode structureincluding a tubular element fused to the end of the envelopeat 9. Acone-shaped electrode shell is shown at 11 and plural lead-in wires 12connected therewith pass through a slightly enlarged bulbous section 13whose inner area forms the closed chamber or reservoir 14 for themercury, and thence through a flat press seal 15.

The valve-like arrangement which forms the inner wall of the cavityincludes one or more cup-shaped partitions, each having a relativelyfiat wall section 16 and an annular flange 17 which is curved in crosssection as shown at 20 (Fig. 3). The peripheral edge or rim 21 of thisflange is of scalloped contour and has a plurality of spaced, in-

wardly extending recesses 22 which are generally U- shaped in crosssection as noted in Fig. 2. When viewed from the side these recessesleave land portions 23 forming arcs of a circle of approximately thesame diameter as the inner diameter of the tube.

Each land portion has a recess or dimple 24 on the curved portion 23 ofthe flange, the dimple being located substantially centrally of the landportion and extends to and partially into the flat section of wall 16.When a plurality of these cups are used, which is preferred in order toprevent any substantial leakage of liquid mercury from chamber 14 intothe central body of the tube, they are arranged in nested relation withthe U-shaped recesses 22 of the inner cup, shown at 26, positioned inthe dimples 24 of the outermost cup shown at 27.

The base wall is formed with a central opening 30 through which Wires 12pass and if desired the wires may be secured therein by fastening meansor they may be sealed therein.

A globule of mercury is shown at 31 in chamber 14 and if the tube 7 isrotated clockwise from the position of Fig. l the mercury travels downthe now inclined wall of the chamber and is, in effect, scooped up bythe first cup 27. A small particle of mercury may pass through a recess22 but it becomes entrapped in the second cup since the land portionthereof lies in line with the recess in the first cup through which themercury travels. Thus the land portion of the second cup simply scoopsup the droplet and deposits it in the second cup. If the tube isreturned to the position of Fig. 1 and tilted somewhat farther so thatthe left-hand end is lower than the opposite end, the tube may be tappedand the droplet will return to chamber 14. The curved face of thepartition 26 thus forms, together with the wall of the tube, theelements of the larger end of a funnel and when the electrode is sotapped the mercury moves through the small channels and into thereservoir. The opposite ends of the channels leading into the reservoirthus correspond to the small end of a funnel and return fiow of themercury to the area containing electrode shell 11 is largely prevented.This is due in some degree to the small openings at these opposite endsof the channels. If a small particle of mercury does pass through thechannel of partition 27 it is generally scooped up into the cup ofpartition 26 as earlier referred to.

Th dimples 24 serve largely as useful indexing means for lining up therecesses 22 of one cup with the land portions 23 of the next cup duringassembly. They also serve the purpose of preventing relative rotationbetween the cups.

In the modified cup shown in Figs. 4 and 5 the recesses 22' are deeperthan those shown in Fig. 2 but the other elements are the same.

Fig. 6 shows the application of the invention as ap plied to a hotcathode mercury lamp wherein the electrode is incorporated into theterminal of the tubular envelope 40. A glass stem 41 having lead-inwires 42 is mounted at the end of the tube and a cap 43 is secured inplace. The wires pass through a pressed glass seal 44. The filament isshown at 45 and the partitions are shown at 46 and 47. An externalcontact 48 is connected with the wires.

The cup-like structures which form the partition shown in this Fig. 6does not have the scalloped periphery. If the inside diameter of theglass wall is only slightly larger than that of the cup, for example,only about ,4,; inch larger, then the bulk of the mercury will still beretained in the cavity during ordinary handling. Also any excess mercurywhich may get into the body of the lamp may be returned to the cavity bya tapping operation as described above. In other words, this cup shapehaving a smooth circular periphery will function to provide greaterresistance to the flow of mercury in one direction than in the other,even though it does not have certain addi ional advantages provided bythe cup with the scalloped periphery. It should be noted that it isadvisable to fasten this smooth type of partition on the wires by meansof a ceramic cement or otherwise, inasmuch as the smooth periphery isnot as well suited to a friction fit with a range of glass diameters asis the sealloped periphery. A globule is shown at 50 in the cavity 51.Insulation for the wires passing through the partitions is shown at 53.

A thin wall small diameter insulating tube of glass is shown at 54 inFig. 7. This glass tube surrounds the wires and serves to elfectivelyinsulate them from the metal cups 26 and 27. The insulating tube isslightly enlarged or flared at the end 55 to prevent the metal cup 26from making contact with the metal electrode shell 11. This glassinsulating tube prevents any part of the gas discharge current fromtaking place on the surface of the cups, as can happen under certaincircumstances if they are part of the metallic circuit. Such dischargefrom the cups may not only produce unsightly sputter of the metal butmay also tend to cause excess heating of the cups and too rapidevaporation of the mercury from the cavity.

It will be apparent that for certain lamps it may be desired to providea better insulated or cooler cavity in order to maintain a more nearlyoptimum temperature therein for the mercury vapor. One way by which thiscan be accomplished is by moving the electrode shell or the filament,both of which generate heat, farther from the end of the tube. Thefarther the filament or the electrode shell is from the partition theless heat will be transferred to the cavity, which reduces the vaporpressure of the mercury. Using a multiplicity of the partitions of thisinvention is another way of improving the insulation and reducing thetemperature of the cavity.

The term electrode is used herein and in the appended claims todesignate both the separately fabricated terminal structure which may befused to the end of a tube as shown in Fig. 1, and also to refer to theentire terminal assembly of a hot cathode lamp where the filament ismounted on a stem and the stem sealed into a tube or bulb as shown inFig. 6.

In either case there is provided a reservoir for the liquid mercurywhich is defined at its inner end by the partition of the presentinvention. The metallic terminal or cathode from which the electricalcurrent flows into the gas in the tubular envelope lies outside thereservoir. This terminal is the cone 11 of Fig. 1 and the filament ofFig. 6.

While there have been described herein what are at present consideredpreferred embodiments of the invention, it will be obvious to thoseskilled in the art that many modifications and changes may be madetherein without departing from the essence of the invention. It istherefore to be understood that the exemplary embodiments areillustrative and not restrictive of the invention, the scope of which isdefined in the appended claims, and that all modifications that comewithin the meaning and range of equivalency of the claims are intendedto be included therein.

What we claim is:

1. An electrode for a mercury discharge tube which is provided with aseal at its outer end and lead-in wires passing through the seal, saidelectrode comprising a tubular envelope which is generally circular incross section and which has a cavity for liquid mercury at said sealedend, and a partition mounted in the tubular envelope with a friction fitdefining the other end of the said cavity, said partition comprising acup-shaped memher with a base and a resilient rim and having said rimfacing the cavity, the outer periphery of the rim having a plurality ofinwardly extending recesses forming channels between the partition andthe envelope and increasing the resilience of the rim, said channelsbeing large enough to permit passage therethrough of liquid mercury pastthe corner sections formed at the juncture of the base and the rim, andinto the cavity, and small enough to cause substantially all liquidmercury traveling in the opposite direction to roll over the rim andpass into the cup-shaped interior of the partition.

2. An electrode for a mercury discharge tube which is provided with aseal at its outer end and lead-in wires passing through the seal, saidelectrode comprising a tubular envelope which is generally circular incross section and which has a cavity for liquid mercury at said sealedend, and a partition defining the other end of said cavity, saidpartition comprising a plurality of cup-shaped members, each providedwith a base and rim and having said rim facing the cavity, the outerperiphery of the rim being of such diameter as to resiliently engage theenvelope and having a plurality of inwardly extending recesses formingchannels between the member and the envelope, said cup-shaped memberbeing arranged in nested relation with the recesses in one offset fromthe recesses in the other, said channels being large enough to permitpassage therethrough of liquid mercury past the corner sections formedat the juncture of the base and the corner sections formed at thejuncture of the base and the rim, and into the cavity, and small enoughto cause substantially all liquid mercury traveling in the oppositedirection to roll over the rim and pass into the cup-shaped interiors ofsaid cup-shaped members.

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